1. Field of the Invention
The invention relates to printed circuit card holders.
2. Description of the Prior Art
Printed circuit cards or boards have been used for many years in electronic equipment. Such boards have the virtue of allowing many electrical devices and components to be readily connected by metallic pathways formed on one or more surfaces of the board. Increasingly, modern day electronic equipment manufactures have turned to plug-in module boards, representing whole sub-systems of electronic apparatus such as an amplifier, counter, or power supply, to aid in equipment assembly and diagnostic trouble-shooting. Generally, such circuit boards are provided with a plurality of electrical contact pads or connections along one edge of the card. The entire board is then press-fitted into a specially designed edge connector having a plurality of mating contacts. Electrical connection between the card edge connector and other devices in the electrical apparatus is generally made through means of separate wiring, or as is more common, by means of multi-wire flat cable.
Though printed circuit (PC) cards or boards are press fitted into card edge connectors generally these connectors do not grip the edge of an inserted board with any appreciable strength. Additionally, a PC card may need to be mounted horizontally, vertically, or in some other configuration, or be subject to vibration as in an aircraft environment. The prior art has recognized that some form of support and retention means must be provided in order to securably hold a PC board in position in its associated card edge connector. Since it is ordinarily convenient to have all PC cards near each other in electrical apparatus prior art PC board supports or holders have generally taken the form of a box-like frame or cage for housing a plurality of PC cards. Usually all the card edge connectors are parallely mounted along one side of the cage, generally known as the back-plane, for convenience in wiring or interconnection between these card edge connectors. Prior art apparatus generally have associated with each card edge connector a pair of U-shaped channels for guiding and supporting a PC card. PC cards are slipped into these U-shaped channel members which act to keep the PC boards arranged in a spaced apart, parallel facing relationship. A slight air-space between each PC card is necessary to allow circulating air to cool the various electrical devices mounted on the PC cards.
It has been recognized by prior art workers that it is not enough to merely guide and support the PC cards, but that each card must be securely fastened or held within its U-shaped channel in order to ensure that a proper electrical connection is made at all times between the PC card connection pads and its associated card edge connector.
The prior art has attempted to overcome this problem by providing releasable locking means associated with the PC cards or their guides for securely holding the PC cards within the guides, while still allowing a mounted PC card to be readily removed from the card cage. These locking means have taken various forms. For instance, U.S. Pat. Nos. 3,853,379, 3,767,974, and 3,764,857 disclose the use of a camming lever locking means provided on the outward ends of each channel-type guide engagable with the outer corners of its associated PC card. Another version of this same concept, shown in U.S. Pat. No. 3,798,507 uses a camming lever locking means provided only on the outward corners of the PC card. Another type of camming lever locking means is shown in U.S. Pat. No. 3,784,954 in which levers having an arcuate slot formed therein disposed near the card edge connector engage a bolt provided near the connection pad end of the PC card. However, the above types of locking PC card supports all suffer from the obvious disadvantages of being relatively complex to manufacture and assemble and requiring at least two locking means to securely hold each PC board. Additionally, most of these types of prior art devices require a special or modified type of PC board to be used with the locking and guiding means.
Another type of PC card support arrangement is shown in U.S. Pat. No. 3,863,113 in which separate, movable wireform card guides mounted upon transverse rods are used to hold inserted PC cards. The ends of the wireform guides hook over the outer corners of the PC cards. However, this arrangement requires a specially shaped corner on the PC card and still requires two wireform guides for each PC card to be mounted. Similarly, U.S. Pat. No. 3,741,513 shows separate, movable and resiliently bowed U-shaped channel members which act to support and retain an inserted PC card. However, this device suffers from the disadvantage that in high vibration environments (e.g. aircraft) an inserted board may still move parallel to the card guides and work as way out of its associated card edge connector.
A final type of PC card support is shown in U.S. Pat. No. 3,715,630 in which a pair of opposing flexible latching members are mounted on a U-shaped card guide and have a cut-out formed on their outer ends for releasable engagement with the corners of an inserted PC card. However, this device suffers from the disadvantage of requiring a pair of latching devices and a pair of associated U-shaped channel guides for each PC card to be mounted.